This invention relates to catalysis, and particularly to hydrocarbon hydroprocessing catalysts, such as those utilized to catalyze the reaction of hydrogen with organosulfur, organonitrogen, and organometallic compounds. More particularly, this invention is directed to a process for utilizing catalysts for hydrodesulfurizing hydrocarbon liquids.
In a typical hydrocarbon refining process, portions of contaminant metals and sulfur components contained in a hydrocarbon oil ordinarily are deposited on porous refining catalysts, causing a loss of catalytic activity and stability as well as selectivity for yielding an intended product. Residual petroleum oil fractions, such as the heavy fractions produced in atmospheric and vacuum crude distillation columns, are especially undesirable as feedstocks for most catalytic refining processes due to their high metals and sulfur content. Economic considerations have recently provided new incentives for catalytically converting the heavy fractions to more marketable products. However, the presence of high concentrations of sulfur and metals, the latter often being found in relatively large porphyrin molecules, precludes the effective use of residua as feedstocks for cracking, hydrocracking, and similar catalytic refining operations.
Methods are available to reduce the sulfur and metals content of residua. One such method is hydrodesulfurization, a process wherein a residuum, usually containing the bulk of the asphaltene components of the original crude from which the residuum was derived, is contacted with a catalyst usually containing hydrogenation metals on a porous refractory oxide support under conditions of elevated temperature and pressure and in the presence of hydrogen, such that the sulfur components are converted to hydrogen sulfide while the metals are simultaneously deposited on the catalyst. However, the deposition of contaminant metals on the catalyst causes deactivation of the catalyst, and, in the usual instance, the extent of deactivation is a function of the amount of metals deposition on the catalyst surface and in its pores, i.e., the usefulness of the catalyst steadily decreases as the amount of deposited metals increases with continued treatment of the residuum.
It has been recognized that typical hydroprocessing catalysts, especially those utilized for hydrodesulfurization purposes, have specific pore size characteristics effective for catalytic processing of residuum. For example, a catalyst employed in a two-catalyst hydrodesulfurization process ordinarily includes at least one desulfurization catalyst having a sizable number of pores of diameter less than 100 angstroms. Although such a catalyst often exhibits high desulfurization activity for a relatively short period of time, its usefulness, i.e. life, is manifestly short in the absence of a catalyst effecting metals removal. The hydrodesulfurization process disclosed in U.S. Pat. No. 4,048,060 is typical of a two-catalyst process employing a first catalyst of relatively small pore characteristics (i.e. some pore diameters less than 100 angstroms) for desulfurization and a second catalyst additionally effecting metals removal. Moreover, U.S. Pat. Nos. 3,931,052 and 4,328,127 disclose catalysts that have specific pore size distributions and are employed in processes involving demetallation of petroleum oil; however, both teach the use of catalysts in combination with catalysts having some pore sizes less than 100 angstroms.
Catalytic hydroprocessing of hydrocarbons presently involving multiple reaction zones provides only limited improvement to such problems as catalyst activity before desirable characteristics such as catalyst stability (i.e. life) are adversely affected. A need still exists for an improved combination of hydroprocessing catalysts having specific pore size characteristics, better surface characteristics, improved feedstock diffusion capabilities, and the like.
It is, therefore, a major object of the present invention to provide a process utilizing a combination of hydroprocessing catalysts and specifically, to provide a process for the catalytic hydroprocessing of a hydrocarbon oil utilizing two catalysts having beneficial pore size characteristics.
It is another object of the invention to provide an improved process for the catalytic hydrodesulfurization of a hydrocarbon oil, and more specifically, to provide a process for the hydrodemetallization and hydrodesulfurization of heavy hydrocarbon oil fractions.
It is a further object still to provide an improved process for hydrodemetallizing a hydrocarbon oil while maintaining a high degree of desulfurization.
A further object of the invention is to provide hydrocarbon products of reduced metals content so as to extend the life of downstream refining catalysts.
These and other objects and advantages of the invention will become apparent from the following description.